Summary

Summary Developmental BIOLOGY & GENETICS - Lectures part 2 (B-B3OBG05)

1 purchase

Course
Ontwikkelingsbiologie En Genetica (BB3OBG05)

Institution
Universiteit Utrecht (UU)

Very extensive lecture notes of all lectures of part 2 of developmental biology and genetics. The notes are in English (just like the course)

[Show more]

Preview 4 out of 50 pages

View example

Uploaded on April 10, 2021
Number of pages 50
Written in 2020/2021
Type Summary

developmental biology
developmental biology
genetics
lectures
zebrafish
developmental biology and genetics
c elegans

Institution
Universiteit Utrecht (UU)
Education
Biologie
Course
Ontwikkelingsbiologie En Genetica (BB3OBG05)

EvaTun

Member since 5 year 80 documents sold

$9.69

Add to cart

Add to wishlist

100% satisfaction guarantee
Immediately available after payment
Both online and in PDF
No strings attached

Hoorcollege 10: Drosophilia germline stem cells

Drospohilia melanogaster
- has a short life cycle (10 days)
- is very easy to grow
- has an extensive background in genetics
- is a multicellular organism
- has very conserved molecular processes and pathways

Genetics
Forward genetics
- Mutant screens
o Chemical mutagenesis
o Transposon insertions

Reverse genetics
- Overexpression
- Transposon local hopping to create imprecise excisions: deletions
- RNAi: expression of hairpin transgenes
- “knock out” by CRISPR/Cas9

There are many genetic tools:
- Markers, balancers
- Expression of genes in specific tissues and at different times
- Clonal analysis

Drosophila as a genetic system: each tissue can be a model system for different processes

Stem cells
External signals: niche provides signals / intrinsic signals: stem cell lineage

Drosophilia males can be recognized by the testis located at the tip of the abdomen, dark
dome like structure. Females lack this and have a vaginal plate.
- Abdomen is also where the germline stem cells lay. Stem cells can become germ cells
or support cells that surround the germ cells.
- Stem cells undergo asymmetric division
- Signaling from the niche
- One cell will have a different cell fate than another

,Female germline
In the ovaries, one cell will differentiate into an oocyte when it comes near the exit

- One unit is called a germarium, the more it progresses it will be called an egg
chamber.
- Stem cells locate at the tip (germarium side). You could prove this by preforming a
transplant of the tip of the ovarioles into a different female. It will give rise to eggs
and adult flies. You could also preform an ablation experiment in which you remove
it.

There are 3 stem cells in the Drosophila ovariole:
- Germ line stem cell (GSC) will give rise to eventually
oocyte and another stem cell, cystoblast (CB)
- Escort stem cells (ESC) will give rise to escort cells
that escort stem cells and will provide factors that are
needed for the differentiation of the cystoblasts
- Follicle stem cells (FSC) will give rise to follicle cells
(FC) which surround an egg chamber and are need for
pattering the oocyte.

The Cap cells are the niche for the GSC

What signals are required to maintain GSCs?
- Notch? Wnt? BMPs?

Stem cell niche GSC:
- Niche: specific location in a tissue where sperm cells can reside for an indefinite
period of time and produce progeny cells while self-renewing
- A small number of stem cells are anchored to their stromal partner cells that produce
signals
- The niche produces micro environmental factors
- Oriented cell divisions direct stem cell daughters away from the stem cell
microenvironment or niche

In dpp temperature sensitive mutants they have found that
the mutant becomes sterile. The germline marker will
disappear in the niche.
➔ Dpp is a BMP and it is required for the germline
stem cell fate.

,What is dpp?
Dpp/TGFbeta/BMP activate Smads. It is a secreted ligand and it binds to a receptor
heterodimer. The receptor complex phosphorylates Smad. Smad can associate itself
with CoSmads en together they translocate to the nucleus and regulate transcription of
Dpp target genes.
➔ Phosphorylated Smads are markers for dpp signaling.

One of the target genes of dpp is bag-of-marbles (bam). In the wildtype bam-GFP is
on in all the stem cells, when these cells want to differentiate, they need bam
expression. In a bam mutant with bam-GFP you still see small green cells because GFP
is expressed under influence of the bam promoter, there is no differentiation into
cystoblasts. You will only see GSC (that are not able to differentiate) and no cysts or
egg chambers. Overexpression of Dpp has similar phenotype as bam mutant because
overexpression causes a negative feedback to bam. In overexpression this causes a repression
of bam this will also cause a loss of oocytes because they can’t differentiate.
➔ Dpp suppresses bam

GSC is associated with Cap cell and receives Dpp signal from this Cap cell and it represses
bam. Smad complex translocates to the nucleus of GSC and
interconnected daughter. Smad complex binds to silencer
complex of bam gene and represses transcription. After division
the two cells will pinch off. No connection between GSC and
cystoblast. The cystoblast is now pushed away. It is out of the
influence of the Cap cell and does not receive Dpp signaling
anymore which causes bam transcription to be turned on.
➔ When cytokinesis is completed bam becomes de-
repressed and initiate cystoblast differentiation

How is Dpp/BMP expression regulated?
Dpp/BMP is produced by the Cap cells. Cap cells are next to terminal filament cells.
➔ Do terminal filament cells regulate Dpp expression?

Unpaired is a secreted ligand secreted by the terminal filament cells. Unpaired is a ligand of
the JAK/STAT pathway.
JAK/STAT: Janus Kinase-Signal Transducers and Activators of Transcription. It is conserved
in Drosophila, except for the ligand.
- Ligand is Unpaired (Udp), not a cytokine as in mammals
- Receptor is Domeless (DOME)
- Kinase associated with receptor is JAK:Hopscotch (HOP)
- Transcription factor is STAT:STAT92E

Which experiments can be done to prove involvement in a process?
- Loss of function mutants
o You expect there to be no germline stem cells and no Dpp
pathway activation.
- Gain of function mutants or ectopic expression
o You expect there to be more germline stem cells and more or
ectopic Dpp pathway activation.

, Ectopic expression can be done with the use of genetic tools
- Generate transgenic line by P-element mediated transformation
- Tissue specific expression by GAL-4/UAS

Ectopic expression of unpaired induces ectopic phosphorylated Smad in the ovary.
➔ Dpp signaling

Signaling in the female GSC niche: Unpaired produced from the Terminal filament cells
activate JAK/STAT signaling in Cap Cells. Cap cells will produce BMP ligands. Dpp
signaling in GSC represses bam and differentiation

Early oogenesis in the germarium
- Egg chambers are generated in the germarium
- Region 1: asymmetric divisions of germ line stem cell
o New germline stem cell
o Cystoblast:
▪ 4 rounds of incomplete divisions to form 16 interconnected cells
▪ Cystocystes
- Region 2: one cell differentiates as the oocyte in the egg chamber, the others become
nurse cells
- Region 3: oocyte becomes polarized and nurse cells start to polyploidize (doubles
DNA but does not pull them apart)

Interconnected cells in the Drosophila germline
- During the first incomplete division cells are connected by
ring canals and a fusome plug forms
- Fusome
o Small membranous vesicles kept together by
components of cytoskeleton
o Anchor one pole of the mitotic spindle
- During the next divisions new fusome plugs will form which
will fuse with the previous one
- One cell will become the oocyte and 15 cells will be nurse
cells, they will dump maternal product into the oocyte and the
nurse cells degenerate. The maternal products pass through
the ring canal. Maternal products are needed for development,
because it does not have any cytotic transcription yet.

Microtubules are bundles that run through the ring canal. Microtubule motors ‘walk’ along
microtubule cables
- Dynein moves towards the minus end
- Kinesin moves towards the plus end
Cargo is transported along the microtubules. Maternal mRNA localization by microtubules

What determines Anterior/Posterior polarity in the oocyte?
Drosophila par-1 is required for localization of posterior determinants. Polarization by par-1
is in response to signaling from posterior follicle cells.

The benefits of buying summaries with Stuvia:

Guaranteed quality through customer reviews

Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.

Quick and easy check-out

You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.

Focus on what matters

Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!

Frequently asked questions

What do I get when I buy this document?

You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.

Satisfaction guarantee: how does it work?

Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.

Who am I buying these notes from?

Stuvia is a marketplace, so you are not buying this document from us, but from seller EvaTun. Stuvia facilitates payment to the seller.

Will I be stuck with a subscription?

No, you only buy these notes for $9.69. You're not tied to anything after your purchase.

Can Stuvia be trusted?

4.6 stars on Google & Trustpilot (+1000 reviews)

69052 documents were sold in the last 30 days

Founded in 2010, the go-to place to buy study notes for 15 years now

Start selling

Summary

Summary Developmental BIOLOGY & GENETICS - Lectures part 2 (B-B3OBG05)

Document information

Subjects

Written for

Seller

Reviews received

Content preview